The present invention generally relates to cooling of liquid food products and, more particularly, is concerned with a heat exchanger employing improvements which enhance its flow, sealing and sanitary characteristics for improved operating efficiency in cooling such products.
One general type of heat exchanger used in chilling, or cooling, a wide variety of liquid food products, such as crushed grapes, orange pulp and the like, employs an elongated cylindrical shell having a hollow interior which houses a plurality of tubes arranged parallel to one another. The tubes extend between headers or end plates on opposite ends of the shell. The end plates commonly have cavities or mount U-shaped tubes which communicate with the ends of the tubes for allowing reversal of flow through the tubes.
Typically, a liquid product is pumped into the heat exchanger through an inlet in one end plate and then through the plurality of tubes and end cavities and out of the heat exchanger through an outlet in the same one end plate. Concurrently, a refrigerant is introduced on the shell side which carries the heat off the fluid on the tube side.
In one prior art heat exchanger manufactured and marketed heretofore by the assignee of the present invention, each end plate (or bonnet) is rounded in shape and has a series of generally parallel partitions fixed across its interior side so as to define reversing flow cavities which communicate with the ends of more than two tubes and have much larger cross-sectional flow areas than the tubes. Each rounded end plate also has an annular flange which is attached by a series of bolts to an annular flange on the end of the shell to close the same. The end plate and shell flanges have respective flat faces thereon which are drawn close together so as to compress a flat annular gasket therebetween to seal the shell end as the end plate is attached to the shell.
Typical constructions of other prior art heat exchangers are represented by those disclosed in U.S. Pat. No. 3,030,782 to Karmazin, No. 3,527,290 to Lossing, No. 3,804,161 to Nowak, No. 4,363,355 to Prucyk, and No. 4,474,011 to Nelson et al. The heat exchangers of these patents as well as the one described above in detail each embodies one or more shortcomings. Some are unduly complex and expensive in terms of the number of parts and manufacturing steps needed to construct them. Others are complicated in terms of the gaskets and fittings required to seal them. Still others provide abrupt changes in the cross-sectional areas of the flow reversing chambers at the ends of the shells compared to the cross-sectional areas of the tubes, which increases pressure drop and pumping power requirements. Yet others would be tedious and time-consuming to clean and maintain in a sanitary condition to chill liquid food products.
A significant disadvantage to prior art heat exchangers is the amount of turbulence which is introduced in the chambers where flow is reversed from one tube to another. This turbulence substantially increases the pressure drop of the liquid as it flows from one tube to another, and when this pressure drop is multiplied by the number of flow reversals that occur as the liquid passes through the heat exchanger, its cumulative effect is quite significant. This requires the use of larger pumps, and the higher pressures that result cause leakage and gasket failures.
Consequently, a need exists for improvements in the construction of heat exchangers, especially those intended to be used to cool liquid food products, which will overcome the aforementioned shortcomings without introducing new ones.